INTERSALT, an international cooperative study, has as its basic purpose elucidating the role of nutritional factors in the etiology of contemporary unfavorable patterns of blood pressure (BP) and high blood pressure (HBP) in populations worldwide. With use of highly standardized methodology, data were collected for 10,079 men and women in 52 centers in 32 countries. In the major initial analyses, blood pressure was significantly linked to intake of sodium (Na), to potassium (K) (inverse), body mass, and high alcohol consumption, all findings with important public health implications. The next major round of analyses has two major components: 1. Based on the important findings of an inverse association between urinary markers of protein intake and BP in analyses conducted thus far on 12 of the 52 INTERSALT centers, the first component is to complete the biochemical and statistical analyses for the 52 centers and provide the first large population-based assessment to test the hypothesis of an inverse relationship of dietary protein to BP of individuals (with N= 10,079). This relationship will also be examined across populations having a wide variety of nutritional patterns (N = 52). 2. The second major component for the coming period is to assess the impact protein intake may have on the original INTERSALT findings of a significant relation of Na, K, and Na/K with blood pressure. This component includes investigation of possible interactions of Na, K, and Na/K with protein as well as with other factors shown in INTERSALT to relate to BP. In addition to these main substantive questions, methodologic issues related to assessment of nutritional factors and blood pressure are to be further investigated. The first round of INTERSALT analyses (on electrolytes, body mass, and alcohol) indicated that improved levels of these lifestyle factors on a long term population-wide basis could mean average population systolic pressure lower by at least 5 mmHg. This difference in turn, from longitudinal study estimates, would mean coronary death rate lower by 9% and stroke death lower by 14%. Such an improved lifetime pattern could also mean a significant lessening of the typical rise of pressure with age, e.g., with a 100 mmol/day lower intake of sodium, systolic pressure rise from age 25 to 55 could be lower by 9 mmHg. This would correspond, for example for men age 55, to a coronary death rate lower by 16%, stroke death lower by 23%. Should the findings in the first 12 INTERSALT centers indicating an inverse association of protein intake with blood pressure be sustained in data from the remaining 40 centers, improved levels of protein intake could also be expected to have a biomedically significant impact on blood pressure and subsequent risk of morbidity and mortality.